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Subject Topic: ISAPI Rewrite 2 proxy requests timing out
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brandonga
Newbie


Joined: 02 January 2012
Location: United States
Posts: 2
Posted: 02 January 2012 at 12:05pm

We have an application that has been in production for years and worked very well. Over the last week the
application has become much slower to respond and at times will not respond at all.

This is the architecture
load balancer -> IIS with ISAPI RW (2 servers) -> load balancer -> coldfusion appserver (2 servers)

There are many rewrite rules for manipulating URL's but the following rules proxy back from the webservers to the
appservers:
RewriteProxy (/.*\.cfm.*) http\://192.168.3.253\:8107$1
RewriteProxy (/.*\.cfc.*) http\://192.168.3.253\:8107$1
We were running isapi_rwf_x86_0076.msi on Windows 2003 but I upgraded last night on one of the webservers to
isapi_rwf_x86_0078.msi to see if that would help and still saw the same behavior.

I have isolated that when the problem starts to occur the webservers serve static content very quickly but any
request to .cfm or .cfc is very slow or does not respond at all. I can invoke the URL
http://192.168.3.253:8107/index.cfm for either one of the webservers and it responds very quickly so the
appservers and load balancer are working without an issue.

At times I see queue_timeout issues in the event log but not every time this issue occur, and not near the number
of errors compared to the number of requests we are getting. There is nothing else that I can see to debug and
understand what is happening to the requests. The memory and CPU on the webservers are very low.

It just seems like traffic that should be proxied is getting hung up in ISAPI Rewrite and there is no explanation or
easy way to see exactly what is happening. Is there any other logging I can use to debug this?

Thanks
Brandon
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Anton
Admin Group


Joined: 30 January 2007
Location: Ukraine
Posts: 10519
Posted: 03 January 2012 at 4:25am

Hello, Brandon

Here are several suggestions:

- please check the logs for crashes all along your architecture. Maybe it's some Coldfusion issues.
- please tell what ISAPI_Rewrite proxy settings are set up. Try to play around with them.
- indicate if you are using any authentication or have to perform long POST requests
- as a debugging tool please consider Fiddler

__________________
Regards,
Anton
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brandonga
Newbie


Joined: 02 January 2012
Location: United States
Posts: 2
Posted: 04 January 2012 at 8:22pm

Anton,

Thank you for your suggestions. I have included my responses inline below:

- please check the logs for crashes all along your architecture. Maybe it's some Coldfusion issues.
[brandon: We closely monitored the infrastructure behind the webservers and it was working very well. As I mentioned
above at the time the issue was occurring I could invoke the URL through the load balancer to the appservers from a web
browser running on the web servers and pages loaded very quickly.]

- please tell what ISAPI_Rewrite proxy settings are set up. Try to play around with them.
[brandon:
worker thread limit: 16
active thread limit: 8
queue size: 100
queue timeout: 60000
conn timeout: 60000
send timeout: 30000
rec timeout: 30000
]

- indicate if you are using any authentication or have to perform long POST requests
[brandon: We are not using any type of integrated authentication, we are doing all authentication in the application
server and pretty standard session management. We do allow image uploads through the server so that would be the only
potential long POST operation]

- as a debugging tool please consider Fiddler
[brandon: I have tried Charles, Service Capture, and the built in tools with Chrome. They simply show a request for any
content that is proxied to the backend go out and never come back or take a very long time to come back]

This issue hasn't happened since Sunday but it was impossible to tell what was going on when it happened and if it
happens in the future I am not sure how to track down what is causing it. When it was happening I would restart IIS, the
site would respond well for a minute or two then it would just stop responding. Very few if any of the requests were
making their way through from IIS to our backend and at the same time static content was serving up just fine. While I
can look at the webserver logs I cannot tell what requests are being queued up on in the ISAPI Rewrite proxy. Is there
any way to log the request beginning and end?

Thanks
Brandon
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Anton
Admin Group


Joined: 30 January 2007
Location: Ukraine
Posts: 10519
Posted: 10 January 2012 at 12:47pm

Hello Brandon

Thanks for the info.

It is however still unclear what version of IIS your
servers use - 6 or 7.

If it's IIS7, you may try to make use of Failed Request
Tracing Tool.

In case of IIS6 consider trying
http://www.microsoft.com/download/en/details.aspx?
id=17275

Another important thing is that ISAPI_Rewrite 2 is really
outdated and if you have a possibility, please consider
upgrading to v3 which is more advanced and has better
logging options.

__________________
Regards,
Anton
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